Using a combination of structural techniques, we propose to seek possible histological substrates for cerebral dominance in human cerebral cortex. The program is predicted on the already well established fact that one cerebral hemisphere in man, usually the left, is critical to higher symbolic activities, and particularly to language function. While evidence now exists documenting the fact that thisfunctional asymmetry can be demonstrated as early as the fourth postnatal week, and that this is accompanied by structural asymmetry of parts of the temporal lobe, we are not aware of qualitative or quantitative descriptions of the relevant histological matrix. Through use of several histological methods and computer programs developed for analysis of this type of data, we hope to specify certain structural and connectional differences related to the phenomenon of hemispheric dominance and lateralization of cortical function. On the basis of data gathered during the first twoyears of this study, we are focusing our attention on the histological structure of the posterior portion of the third frontal convolution (Broca's area) and the immediately postjacent segment of the motor strip.